The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is driven by one or more turbojet engine(s) each housed in a nacelle. A nacelle generally has a substantially tubular structure comprising an air inlet upstream of the turbojet engine, an intermediate assembly intended to surround a fan of the turbojet engine and a rear assembly which can integrate thrust reversal means and intended to surround the combustion chamber and all or part of the compressor and turbine stages of the turbojet engine, and is generally ended by an ejection nozzle the outlet of which is located downstream of the turbojet engine.
The modern nacelles are intended to accommodate a bypass turbojet engine capable of generating, on the one hand, a flow of hot gases (also called main flow) coming from the combustion chamber of the turbojet engine and circulating in a space delimited by a compartment of substantially tubular shape called a “core” compartment, and on the other hand, a cold air flow (called secondary flow) coming from the fan and circulating outside of the turbojet engine through an annular passage, also called flow path, formed between an inner structure defining a fairing of the turbojet engine and an inner wall of the nacelle. The two flows are ejected from the turbojet engine by the back of the nacelle.
The “core” compartment comprises an outer envelope serving as a casing and called inner fixed structure (IFS).
This IFS is subjected to high thermal stresses and it is usually protected by using thermal protection panels, thereby insulating the components of the nacelle from the engine environment in order to maintain them at acceptable temperatures and thus extending their service life.
These thermal protections also provide fire protection and can be used in other areas of the nacelle, at which there is a risk of fire.
In order to thermally protect the IFS, it is known to resort to protection panels disposed for example on the “core” compartment side and comprising at least one insulating mat, generally made from silica fibers, ceramics or a microporous material, said mat being sandwiched between sheets generally made of stainless steel.
The thermal protection mats are fastened to the IFS using fastening systems which cooperate locally with the IFS over the entire protection surface, in the manner of rivets. The thermal protection is also retained to the IFS at the edges by retaining strips commonly called “retainers.”
An example of a known fastening system is described in the document FR 2 829 811.
Such a fastening system uses a safety wire system and generally comprises two parts, namely a base fastened in the IFS having a hooking structure (for example a hook, loop or eyelet bolt type) and a retaining button. The hooking structure is disposed in a corresponding fastening opening of the mat, and is capable of receiving a link called a safety wire. The retaining button bears against an outer surface of the mat so as to form a maintaining and clamping washer, the retaining button being provided with passage orifices of the safety wire whose ends are twisted and clamped.
The retaining of the panel on the IFS is thus provided.
In order to improve the fastening, the twisted end of the safety wire is then sealed in silicone.
Alternatively, the safety wire system may be replaced by a threaded or tapped hooking structure cooperating with a complementary end of the retaining button.
In general, the known fastening systems do not provide a sufficient cooling at the attachment points. This is due in particular to the fact that the hooking structures constitute thermal bridges, all the more so since the hooking structures are generally manufactured in a metallic material. In order to overcome this problem, it is generally envisaged to increase the insulation, either by increasing the thickness of the mat or by making said mat of a material contributing to more reliable insulation. However, these solutions are not satisfactory in terms of performance and cost. Furthermore, increasing the thickness of the mat is not always possible.